Heat pads have been used in repair molds to heat tire patches for repairing tires and especially large size tires for trucks and off-the-road vehicles. In the repair of these tires a patch is applied which may include a plug core inserted in the injury. A mandrel may then be inserted in the tire cavity with an airbag and heat pad for pressing and heating the inside of the tire. A heat pad and airbag may then be positioned around the outside of the tire and the tire with the mandrel, airbags and heat pads placed inside a repair mold for spot curing the patch.
Heretofore the heat pads have been heated electrically by coiled nichrome wires sewn in fiberglass and molded in heat-resistant insulating rubber. Due to the high pressure exerted on the heat pads by the air-bags, the heat pads have been deformed and stretched over the curved surface of the annular tire which has caused the nichrome wires to break and curtail the service life of these heat pads. The failure of the heat pads has increased the cost of spot curing and has also resulted in incomplete vulcanization of the tire patches and scrapping of the tires. Also the time required to bring the heat pad up to a temperature where the curing of the patch material will start and the time required to bring the heat pad up to the desired maximum curing temperature has been extended because of the thickness of the heatresistant insulating rubber in which the nichrome coiled wires are embedded.